TRANSGENIC AND KNOCKOUT SHARED RESOURCE PROJECT SUMMARY The main purpose of the Mayo Clinic Cancer Center Transgenic and Knockout (TKO) Shared Resource is to assist investigators at all 3 sites with the design and the generation of genetically modified mouse models. Utilization of the resource has been strong with 49 Cancer Center members from 8 different Programs using the Shared Resource during the current funding period (2013-2017). Our services include CRISPR/Cas9 mediated editing of genes of interest in fertilized mouse eggs to generate knockout and knock-in mouse models to inactivate or tag it, or to introduce point mutations, reporter genes, loxP sites or large deletions. Although gene editing by CRISPR/Cas9 is incredibly useful, in some instances it is not as robust as conventional gene targeting in embryonic stem (ES) cells, prompting us to maintain our classical services mainly to insert large (>5 kb) DNA fragments and loxP sites. Additional services offered by the TKO Core include founder screening, founder breeding, sperm cryopreservation, recovery of cryopreserved mouse strains through in vitro fertilization, and standard histopathology. TKO Shared Resource staff also provide advice on DNA preparation, mouse genotyping, handling and husbandry. To stay at the cutting edge of genome editing, the TKO devotes time and effort to develop or implement innovative and experimental procedures. The above activities allow Cancer Center members to implement state-of-the-art mouse models to address key open questions in the field of cancer etiology and to design and test new therapeutic approaches that improve cancer treatment outcome. The TKO Shared Resource achieved a score of Outstanding at the previous site visit.